Sweden and Finland began the formal process of joining Nato on Wednesday morning when their ambassadors to the alliance submitted signed letters of application to the alliance on Wednesday morning.
Nato secretary general Jens Stoltenberg said it was an "honour" to accept the letters of application personally from Sweden's ambassador to Nato, Axel Wernhoff, and the Finnish representative, Klaus Korhonen.
"This is a good day at a critical time for our security," he told them at Nato headquarters near Brussels. "Your applications are a historic step."
The move follows weeks of heated debate in the two countries since Russia's February 24th invasion of Ukraine leading to parliamentary debate and formal government decisions in the last days.
However, the accession process did not move forward any further after Turkey, which earlier had outlined a broad list of complaints with alliance members, blocked the formal acceptance of the applications.
Nato ambassadors met on Wednesday morning, but could not agree to proceed with the applications after Turkey held up consensus, according to people familiar with the matter. Only after all Nato allies give consent can Sweden and Finland start accession talks with the alliance.
Turkish president Recep Tayyip Erdogan signalled earlier this week that he would not allow the Nordic nations to join, alleging they support Kurdish militants his government regards as terrorists. He added on Wednesday that his concerns extend beyond Sweden and Finland but also to how other Nato members handle the Kurdish groups.
US president Joe Biden said the United States strongly supports the two countries joining Nato and will work to quickly bring them into the alliance.
While the applications are considered, the US “will work with Finland and Sweden to remain vigilant against any threats to our shared security, and to deter and confront aggression or the threat of aggression”, Mr Biden said ahead of a Thursday visit by the Finnish and Swedish leaders.
Prior to Turkey’s concerns, Nato ambassadors were expected to rapidly accept the bids in what was seen as a minor formality and sign the accession protocols within days of their applications. That timing is now set to slip as it is unclear how long Turkey will dig in over its demands.
"We haven't lost the possibility of a fast-track process," Finnish president Sauli Niinisto told reporters in Stockholm on Wednesday.
Turkey is engaged in talks with Sweden and Finland, and Nato members say they are confident the Turkish concerns can be overcome. After a phone call with Turkish foreign minister Mevlut Cavusoglu, Mr Stoltenberg described Ankara was "a valued ally and any security concerns need to be addressed, we must stand together at this historic moment".
With Finland and Sweden now in the so-called “grey zone”, between formal application and accession, leading Nato allies have stated publicly their readiness to defend the two Nordic countries in this interim period.
After signing mutual defence agreements with the US and UK, German chancellor Olaf Scholz has vowed to "increase our military co-operation, in particularly in the Baltic Sea region and through joint exercises".
Many foreign vessels are en route to the Baltic region to participate in upcoming Nato exercises between June 5th-6th, while US warship the USS Kearsarge is en route to Stockholm to “work with allies and partners in ensuring security and stability the region”.
– Additional reporting: Bloomberg